The insulation material industry has determined that it is desirable to utilize fibers in thermal, electrical and acoustical insulating applications, which do not persist in physiological fluids, that is, fiber compositions which exhibit a low biopersistence or a high solubility in physiological fluids. While candidate materials have been proposed, the use temperature limit of these materials have not been high enough to accommodate many of the applications to which traditional high temperature resistant alumino-silicate fibers are applied.
Many compositions within the synthetic vitreous fiber family of materials have been proposed which are non-durable or decomposable in a physiological medium.
The high temperature resistant fibers should also exhibit minimal linear shrinkage at expected use temperatures, and after prolonged or continuous exposure to the expected use temperatures, in order to provide effective thermal protection to the article being insulated.
In addition to temperature resistance as expressed by shrinkage characteristics that are important in fibers that are used in insulation, it is also required that the fibers have mechanical strength characteristics during and following exposure to the use temperature, that will permit the fiber to maintain its structural integrity and insulating characteristics in use.
One characteristic of the mechanical integrity of an inorganic fiber is its after service friability. The more friable a fiber, that is, the more easily it is crushed or crumbled to a powder, the less mechanical integrity it possesses. In general, inorganic fibers that exhibit both high temperature resistance and non-durability in physiological fluids also exhibit a high degree of after service friability. This results in the fiber lacking the strength or mechanical integrity after exposure to the service temperature to be able to provide the necessary structure to accomplish its insulating purpose. Other measures of mechanical integrity of fibers include compression strength and compression recovery.
Thus, it is desirable to produce an improved inorganic fiber composition that is readily manufacturable from a fiberizable melt of desired ingredients, which exhibits low shrinkage during and after exposure to service temperatures of 1400° C. and greater, which exhibits low brittleness after exposure to the expected use temperatures, and which maintains mechanical integrity after exposure to use temperatures of 1400° C. and greater.